Hello, I’m a fifth grader at IV Elementary and I
was wondering what decomposition is all about. Is
decomposition important for the ecosystem, and
how/why does it work? I’ve heard that nitrogen has
something to do with it, and I’m wondering why
that’s important. Thank you!

Question Date: 2018-11-02

Answer 1:

Great question! You are right on track in your
thinking - decomposition does indeed have
something to do with nitrogen and ecosystems!

If you have been studying ecosystems, you have
probably learned about the water cycle, the
carbon cycle, the nitrogen cycle and the
phosphorous cycle (the last one being
representative of the "mineral" cycles).

Nitrogen is a key component of many compounds
in living organisms - especially in the
proteins of plant and animal bodies. But
most of the nitrogen is in the atmosphere (about
78% of the atmosphere is nitrogen) - how is it
converted into a form that living organisms can
use? It turns out that most of it is
available because of some specific kinds of
bacteria - which can "fix" the atmospheric
nitrogen. The best "fixers" are symbiotic
bacteria that live with the roots of legumes
(plants like peas and beans). So, in a healthy
ecosystem over many years, there is plenty of
nitrogen available for plants and animals to use.

But more to your question - what about
decomposition? In some ways, you could
consider decomposition as a type of nitrogen
recycling. When living things die, they
decompose. But what does that mean? The
proteins in the plant or animal that has died are
made of amino acids - and there is a lot of
nitrogen in those proteins. Bacteria and
fungi have the ability to break down
those proteins (that is the "decomposition"
action) and use the amino acids to make their
own, new proteins. In this process, they release
any excess nitrogen in the form of ammonium
(NH4+) . Other bacteria can convert
the ammonium to soil nitrates and nitrites which
can then be absorbed by plants. The plants
get eaten by animals, which use the nitrites and
nitrates to make their own proteins.... the
animal dies and the cycle starts over.

However, as in most recycling operations, the
savings is not 100%. A certain amount of nitrogen
is steadily lost back to the atmosphere in a
process called denitrification (again,
specific kinds of bacteria convert the nitrates
and nitrites to nitrogen gas or nitrous oxide).
But the nitrogen fixers can recapture it and start
it all over again by converting it to ammonia and
nitrates.

Keep asking great questions! It's really great
that you are thinking about how certain processes
are connected - this is called a "systems
approach" to a biological question and it
allows you to think about how even small changes
in one part of the system can have major effects
on another.